1. Field of the Invention
The present invention relates to a pressure cylinder and more particularly, to a pressure cylinder, which has a hidden loop design.
2. Description of the Related Art
The so-called pressure cylinder is a combination of an air cylinder and a hydraulic cylinder, which mainly uses a piston rod of the air cylinder to compress a hydraulic fluid in giving a pressure to a piston rod of the hydraulic cylinder, thereby enhancing the output force of the piston rod of the hydraulic cylinder.
However, in all conventional pressure cylinder designs, the applied compressed gas is flowing through a loop formed of external pipelines. After a long use, the external pipelines may be oxidized and deteriorated. Therefore, the pipelines must be regularly replaced. Further, the connectors connecting the pipelines may be loosened easily, causing a gas leak. All these problems may lead to machine failure, or even industrial accidents.